JP5788643B2 - Glass substrate - Google Patents

Description

  The present invention relates to a glass substrate used in various apparatuses, particularly low specific gravity, high Young's modulus, excellent fracture toughness, extremely smooth surface roughness after processing, head sliding characteristics, impact resistance characteristics. The present invention relates to a glass substrate for an information recording medium having excellent physical properties necessary for future use of an information recording medium substrate, which is excellent in adhesion of an abrasive and glass sludge to the substrate surface.

  In the present invention, the “information recording medium” means an information magnetic recording medium that can be used in hard disks for various electronic devices.

  In recent years, large amounts of data such as moving images and sounds have been handled in personal computers and various electronic devices, and large-capacity information recording apparatuses are required. As a result, the demand for higher recording density is increasing year by year for information recording media.

  In order to cope with this, the adoption and mass production of the perpendicular magnetic recording system are being promoted. In this perpendicular magnetic recording system, the substrate is required to have higher levels of heat resistance and surface smoothness than the current substrate. It also has a low specific gravity to reduce the burden on the spindle motor, a high mechanical strength to prevent disk crashes, and a high fracture toughness that can withstand the impact with the head when dropped. More important.

Examples of the material used for the information recording medium substrate include an Al alloy, glass, and crystallized glass. Glass materials such as amorphous glass and crystallized glass are superior to Al alloys in that they have higher Vickers hardness and higher surface smoothness, and are currently widely used in applications that are expected to be used dynamically.
However, since glass is generally brittle, there is a characteristic that the substrate is easily damaged by a slight scratch on the substrate surface. Especially in information recording media substrates used in next-generation hard disks, the magnetic disk rotation speed tends to increase with the increase in recording density, so cracks based on slight scratches on the substrate surface Resistance to propagation, that is, fracture toughness is a particularly important evaluation item, and it is required to have high fracture toughness.

In addition, for substrates that can be used for media film formation, particularly glass substrates, there is a need to reduce the distance between the head and the media in accordance with the recent increase in storage density, and the head flying distance of less than 1 nm is supported. Accordingly, it is required that the value of Ra as a surface roughness index of the substrate is less than 1 mm and the value of μWa is less than 0.8 nm.
In addition, as the film deposition temperature rises (> 600 ° C.) corresponding to the future HAMR (Heat Assisted Magnetic Recording) system, the heat resistance of the substrate itself needs to be sufficiently high to suppress the shape change after the heat treatment. is there.

  In addition, the substrate surface before media film formation needs to be extremely clean, and contamination generation factors such as abrasives, glass sludge, and cleaning dirt must be extremely avoided.

  Patent Document 1 discloses a glass substrate for a magnetic disk with a small number of defects fixed to the glass surface as a high recording density magnetic disk substrate. This is manufactured by including a specific additive in the cleaning liquid for cleaning the substrate. However, it is very difficult to achieve the substrate surface cleanliness required in recent years only by preparing such a polishing liquid and a cleaning liquid.

  Patent Document 2 discloses a method for manufacturing a magnetic disk in which the formation of convex defects due to the adhesion of silica particles as an abrasive is suppressed. Also in this document, the adhesion of silica particles is reduced by preparing the polishing liquid, but there is a limit to the reduction in cleanliness as described above. Silica particles are mainly used in the final final polishing (mirror polishing or so-called 2nd poly process), but the occurrence of contamination on the substrate surface is a rough polishing process (so-called 1st 1st) which is a pre-process of final polishing. The main factor is adhesion of cerium oxide particles often used in a process called poly).

Conventionally, contamination that adheres to the surface of a glass substrate is caused by the fact that the adhesion of an abrasive or glass sludge cannot be completely removed through a cleaning process, and is generally removed by acid or alkali in order to remove it. A method of removing the contamination by increasing the concentration of the solution and a method of removing contamination by immersing in a low concentration (0.010 to 0.050 wt%) hydrofluoric acid for a short time have been performed.
Furthermore, the adhesion of contamination has been suppressed by preparing an abrasive or a cleaning liquid.
However, even with such a method, it is difficult to achieve the cleanliness of the substrate surface required as a next-generation information recording medium substrate.
JP 2010-108591 A JP 2009-087441 A

  The purpose of the present invention is to provide various physical properties required for next-generation information recording medium substrate applications typified by a glass substrate that is required for a high level of surface cleanliness for various apparatus applications, particularly perpendicular magnetic recording methods, An object of the present invention is to provide a glass substrate for an information recording medium that suppresses head crashes caused by contamination adherence to the substrate surface in order to cope with higher density and improves the recording / reproducing characteristics after film formation of the medium. In addition, the substrate for information recording media having high fracture toughness, and excellent workability therefor, high heat resistance to meet HAMR that may be required for future increases in recording density, and low-cost molten glass An object of the present invention is to provide a glass material suitable for the direct press method capable of processing a thin plate.

As a result of intensive studies and studies to achieve the above object, the present inventors have controlled the value of the zeta potential of a glass substrate measured under a specific measurement condition to a specific range, and thus are specific to the glass substrate. By controlling the physical properties, it is possible to easily reduce the surface roughness Ra of the substrate after substrate processing such as polishing and cleaning to less than 1.0 mm using conventional processing and cleaning steps. In addition, the inventors succeeded in developing a glass material and a glass substrate in which the amount of contamination adhered to the substrate surface is extremely smaller than that of a conventional substrate.
More specifically, the present invention provides the following.

(Configuration 1)
A glass characterized in that the surface zeta potential measured using an aqueous solution in which Na ₂ SO ₄ is mixed as a buffer and the pH is adjusted to 10 with H ₂ SO ₄ and NaOH is lower than −50 mV. substrate. However, the electric potential of the electrically neutral region of the aqueous solution sufficiently separated from the surface of the glass substrate is set to 0V.
(Configuration 2)
The surface zeta potential measured using an aqueous solution in which Na ₂ SO ₄ is mixed as a buffer and the pH is adjusted to 2 with H ₂ SO ₄ and NaOH is negative. Glass substrate. However, the electric potential of the electrically neutral region of the aqueous solution sufficiently separated from the surface of the glass substrate is set to 0V.
(Configuration 3)
In the potential difference between the substrate surface and the cerium oxide particles measured using an aqueous solution containing cerium oxide particles, mixed with Na ₂ SO ₄ as a buffer, and adjusted in pH with H ₂ SO ₄ and NaOH, the aqueous solution The glass substrate according to Configuration 1 or 2, wherein the minimum value of the potential difference when measured by changing the pH of the solution in a range of 10 to 12 is 20 mV or less.
(Configuration 4)
The potential difference between the surface of the substrate and the silica particles measured using an aqueous solution containing silica particles, mixed with Na ₂ SO ₄ as a buffer, and adjusted to pH ₄ with H ₂ SO ₄ and NaOH is 15 mV or more. The glass substrate according to any one of Configurations 1 to 3, wherein the glass substrate is provided.
(Configuration 5)
When expressed as mol% based on oxide, it contains SiO ₂ and Al ₂ O ₃ as glass constituents,
The R ₂ O component content is 10 mol% or less (R; one or more selected from Li, Na, K), and the R′O component content is 15 mol% or more (R ′; Mg, Ca, Zn, The glass substrate according to any one of configurations 1 to 4, wherein the glass substrate is one or more selected from Ba, Sr, and Fe.

  The glass substrate of the present invention has specific gravity and Young's modulus, Vickers hardness, surface smoothness and high fracture toughness required as a next-generation information recording medium substrate. In addition, the glass substrate of the present invention has good workability in substrate polishing, and the occurrence of contamination on the substrate surface is extremely small. Therefore, this invention can provide the glass substrate for information recording media which has high productivity.

It is the figure which showed the pH dependence of the zeta potential of Example 1 and Comparative Examples 1 to 4 and 7 of the present invention. The figure which showed the pH dependence of the zeta potential of cerium oxide when changing the kind of solution. It is a diagram illustrating a zeta potential of SiO 2 _(colloidal silica) when changing the type of solution. It is an AFM image of Example 1 of the present invention. It is a TEM photograph image of Example 1 of this invention, and the reference line of the figure lower right is 5 nm.

Here, the zeta potential is generally a sliding surface existing around the particle when the particle in the liquid is present and the potential of the electrically neutral region that is sufficiently away from the particle is zero. Is the potential.
When a solution in which particles are dispersed is stored in a measurement cell and an electric field is applied from the outside, the particles are charged (migrated) because they are charged. Since the swimming path speed is proportional to the charge of the particles, the zeta potential can be obtained by measuring the migration speed of the particles. When the electrophoretic light scattering method is used, the migration speed of particles can be obtained from the amount of frequency shift of scattered light due to the Doppler effect.
In addition, when measuring the zeta potential of a flat plate sample, it can be obtained by attaching a flat plate sample to one side of the measurement cell and observing the electroosmotic flow reflecting the surface potential of the flat plate sample in a solution in contact with the flat plate sample. .
The zeta potential can be measured using, for example, a zeta potential / particle size measurement system ELSZ-1 or ELSZ-2 manufactured by Otsuka Electronics Co., Ltd.

  The general polishing process at present is roughly divided into two types, 1P (1st poly) and 2P (2nd poly). In 1P, polishing is performed using alumina, zirconia, cerium oxide, or fixed abrasive. After finishing the surface of the substrate, the substrate is polished so that the surface finally becomes a mirror surface by using colloidal silica at 2P.

  At that time, after polishing in each step, it is necessary to remove the abrasive in the previous step and sludge generated by polishing by moving to the next step after passing through the cleaning step.

In the present invention, the value of the surface roughness Ra of the substrate can be easily controlled by controlling the physical property specific to the glass substrate by controlling the value of the zeta potential of the glass substrate measured under a specific measurement condition within a specific range. It is possible to obtain a glass material that can be made to be less than 1.0 mm and that has a very small amount of contamination on the substrate surface as compared with the conventional substrate.
That is, Na ₂ SO ₄ is mixed as a buffer, and the zeta potential of the surface measured using an aqueous solution whose pH is adjusted to 10 with H ₂ SO ₄ and NaOH is set to a value lower than −50 mV. Here, the electric potential of the electrically neutral region of the aqueous solution sufficiently separated from the surface of the glass substrate is set to 0V.
By setting the zeta potential of the substrate surface measured under the above conditions to a value lower than −50 mV, the difference in zeta potential from the abrasive can be reduced. That is, it is possible to easily obtain a state in which the abrasive is difficult to adhere to the substrate surface.
In order to make this effect easier to obtain, the zeta potential of the substrate surface measured under the above conditions is more preferably lower than −52 mV, and most preferably lower than −54 mV. The lower limit of the potential is preferably 20 mV lower than the zeta potential of the abrasive measured under the same conditions, preferably 15 mV lower than the zeta potential of the abrasive, and most preferably 10 mV lower than the zeta potential of the abrasive.

Furthermore, it is preferable that the zeta potential of the surface measured using an aqueous solution in which Na ₂ SO ₄ is mixed as a buffer and the pH is adjusted to 2 with H ₂ SO ₄ and NaOH is negative. Here, the electric potential of the electrically neutral region of the aqueous solution sufficiently separated from the surface of the glass substrate is set to 0V.
In the polishing process, especially in 2P, the pH of the polishing slurry is sometimes near 2. However, since the zeta potential near pH 2 shows a value near the isoelectric point in the conventional glass substrate, the adhesion of the abrasive Becomes prominent. Therefore, by making the zeta potential of the substrate near pH 2 negative, it is possible to suppress the adhesion of the abrasive or sludge (glass polishing waste) to the substrate surface. In order to make it easier to obtain this effect, the zeta potential of the substrate surface measured under the above conditions is more preferably lower than −5 mV or lower, and most preferably lower than −10 mV or lower. The lower limit of the potential is not particularly limited.

In addition, the glass substrate of the present invention includes a substrate surface measured using an aqueous solution containing cerium oxide particles, mixed with Na ₂ SO ₄ as a buffer, and adjusted in pH with H ₂ SO ₄ and NaOH, and the cerium oxide. In terms of the potential difference from the particles, the minimum value of the potential difference when measured by changing the pH of the aqueous solution in the range of 10 to 12 is preferably 20 mV or less.
The cerium oxide particles are an abrasive mainly used in 1P. In order to improve the dispersibility in the polishing slurry, it is most preferable to adjust the pH of the polishing slurry to the alkali side in terms of polishing efficiency and prevention of reattachment. However, since the potential difference between the zeta potential of the cerium oxide particles per se when the pH of the polishing slurry is alkaline and the zeta potential of the existing glass substrate is large, adhesion of the abrasive is inevitable. Therefore, this can be prevented by adjusting the physical properties of the substrate and setting the potential difference between the substrate surface and the cerium oxide particles under the above measurement conditions to 20 mV or less. In order to make it easier to obtain this effect, the potential difference between the substrate surface and the cerium oxide particles measured under the measurement conditions is more preferably 15 mV or less, and most preferably 10 mV or less.

The potential difference between the surface of the substrate and the silica particles measured using an aqueous solution containing silica particles, mixed with Na ₂ SO ₄ as a buffer, and adjusted to pH ₄ with H ₂ SO ₄ and NaOH is 15 mV or more. The glass substrate according to claim 1, wherein the glass substrate is provided.
It is an abrasive used mainly for 2P of silica particles. Since the silica particles are nano-sized particles, in polishing, it is used mainly in the region where the pH is 2 to 4 because the polishing efficiency is good to be subjected to polishing in an aggregated state in advance. Since the potential difference between the silica particles and the existing substrate is small, adhesion of the abrasive tends to occur. Therefore, this can be prevented by adjusting the physical properties of the substrate and setting the potential difference between the substrate surface and the silica particles to 15 mV or more under the measurement conditions. In order to make this effect easier to obtain, the potential difference between the substrate surface and the silica particles measured under the measurement conditions is more preferably 18 mV or more, and most preferably more than 20 mV.

In order to impart such physical properties to the glass substrate, when the content of the glass constituent component is expressed by mol% based on the oxide, it contains SiO ₂ , Al ₂ O ₃ , and further, the R ₂ O component The content is 10 mol% or less (R; one or more selected from Li, Na, K), and the R′O component content is 15 mol% or more (R ′; Mg, Ca, Zn, Ba, Sr, Fe) It is preferable that it is 1 or more types selected from.
Here, mol% on the basis of oxide means that each component contained in the glass, assuming that oxides, nitrates, etc. used as raw materials for glass components are all decomposed and changed to oxides when melted. This represents the amount of each component contained in the glass, with the total number of moles of the resulting oxide being 100 mol%. Hereinafter, unless otherwise specified, mol% is meant.

The R ₂ O component (where R is one or more selected from Li, Na, and K) is a component that affects the zeta potential of the substrate while lowering glass viscosity, improving formability, and improving homogeneity. is there. Further, by containing the R ₂ O component, it is possible to exchange the alkali metal ions on the surface after forming the substrate and to impart additional characteristics. In order to set the zeta potential of the glass substrate of the present invention to a desired value, the upper limit of the content of R ₂ O component (total of each component of Li ₂ O, Na ₂ O, and K ₂ O) is 10%. Preferably, 9% is more preferable and 8% is most preferable. Further, if the content of the R ₂ O component is less than 1%, it is not possible to obtain an effect such as a reduction in viscosity of the glass. Therefore, the lower limit of the content is preferably 1%. Moreover, reducing the R ₂ O component also has the effect of limiting the precipitation of alkali components on the substrate surface. Since the effect is most remarkable particularly in the Li ₂ O component, it is preferable that the content of the Li ₂ O component is as small as possible or not substantially contained.

The individual contents of each component of Li ₂ O, Na ₂ O, and K ₂ O will be described.
The Li ₂ O component can be optionally contained, but the upper limit is preferably 2%.
The Na ₂ O component can be optionally contained, but the upper limit is preferably 10%, more preferably 9%, and most preferably 8%.
The K ₂ O component can be optionally contained, but the upper limit is preferably 6%, more preferably 4%, and most preferably 1%.
Here, in order to produce a glass substrate from a crystallized glass substrate, the Na ₂ O component causes excessive precipitation of crystals when the desired crystal phase is precipitated as compared with other alkali components. In addition to being a component that easily suppresses the influence, it is an important component for promoting chemical strengthening of the substrate by immersion in molten salt while maintaining good chemical durability of the material.

  The R′O component (R ′; one or more selected from Mg, Ca, Zn, Ba, Sr, and Fe) brings about low glass viscosity, improved formability, and improved homogeneity, while the zeta potential of the substrate. It is a component that affects Moreover, when it is set as crystallized glass, it is a component which comprises a main crystal phase by heat processing of an original glass. In order to set the zeta potential of the substrate to a desired value, the lower limit of the content is preferably 15%, more preferably 18%, and most preferably 20%. On the other hand, when the total amount exceeds 35%, not only vitrification becomes difficult, but also precipitation of insoluble matter and increase in devitrification temperature are caused. The upper limit of the content is preferably 35%, more preferably 32%, and most preferably 26%.

  The ZnO component is one of the components constituting the main crystal phase by heat treatment of the original glass, and contributes to lowering the specific gravity and Young's modulus of the glass and is also effective for lowering the viscosity of the glass. However, if the content is less than 5%, the above effect cannot be obtained. Therefore, the lower limit of the content is preferably 5%, more preferably 6%, and most preferably 7%. On the other hand, if the content of the ZnO component exceeds 20%, the precipitation of crystals from the original glass becomes unstable and the crystal particles are likely to be coarsened, so the upper limit of the content is preferably 20%. % Is more preferred and 14% is most preferred.

  The MgO component is a component that contributes to lowering the specific gravity of the glass and improving the Young's modulus, and is an optional component that can be optionally added to lower the viscosity of the glass. However, if the content is less than 5%, the above effect cannot be obtained. Therefore, the lower limit of the content is preferably 5%, more preferably 6%, and most preferably 7%. On the other hand, if the content of the MgO component exceeds 20%, the precipitation of crystals from the original glass becomes unstable and the crystal particles are likely to be coarsened, so the upper limit of the content is preferably 20%. % Is more preferred and 14% is most preferred.

The FeO component is one of the components constituting the main crystal phase by heat treatment of the original glass, and generates a spinel compound together with the Al ₂ O ₃ component and the TiO ₂ component. Moreover, although it is a compound which acts also as a clarifier, platinum generally used at the time of glass melting will be alloyed. Therefore, the upper limit of the content is preferably 8%, more preferably 6%, and most preferably 4%.

  The CaO component is a component that contributes to lowering the specific gravity of the glass and improving the Young's modulus, and is effective in lowering the viscosity of the glass, so it can be added as an optional component. However, if the CaO component exceeds 10%, the specific gravity of the original glass increases and it becomes difficult to obtain the desired glass. Therefore, the upper limit of the content of these components is preferably 10%, more preferably 7%, and most preferably 4%.

  BaO component and SrO component have the same function as MgO, CaO, etc. as effective components for lowering glass viscosity and improving chemical durability and mechanical improvement, but the glass specific gravity tends to increase. The upper limit of the content is preferably 6%, more preferably 4%, and most preferably 3%.

The SiO ₂ component is an essential component for forming a glass network structure and achieving an improvement in chemical stability and a reduction in specific gravity. If the amount is less than 40%, the resulting glass has poor chemical durability, and the specific gravity tends to increase with an increase in the content of other components, so the lower limit of the content may be 40%. Preferably, 45% is more preferable, and 50% is preferable. Further, if it exceeds 80%, dissolution and press molding are likely to be difficult as the viscosity increases, and the homogeneity and clarification effect of the material are likely to be lowered. Therefore, the upper limit of the content is preferably 80%. 75% is more preferable, and 70% is most preferable.

The Al ₂ O ₃ component is an important component that contributes to stabilization of glass and chemical durability, but if its amount is less than 3%, its effect is poor, so the lower limit of the content is 3%. 5% is more preferable, and 7% is most preferable. On the other hand, if it exceeds 20%, the dissolution, moldability and devitrification resistance deteriorate, and the homogeneity and clarification effect tend to decrease. Therefore, the upper limit of the content is preferably 20%, and 16% Is more preferable, and 12% is most preferable.

The P ₂ O ₅ component has an effect of suppressing the progress of cracks in the glass, and thus can contribute to an increase in Vickers hardness. Moreover, it contributes to lowering the viscosity and can improve the melting and clarifying properties of the original glass by coexistence with SiO ₂ . In order to obtain these effects, the P ₂ O ₅ component can be optionally contained, more preferably 0.1% or more, and most preferably 0.2% or more. However, if this component is added excessively, vitrification becomes difficult and devitrification and phase separation are likely to occur. Therefore, the upper limit of the content is preferably 3%, more preferably 2%, and most preferably 1%. .

In order to obtain a high clarification effect while maintaining the physical properties required for the information recording medium substrate, it is preferable to contain at least one component selected from SnO ₂ component and CeO ₂ component as the main clarification component. . In order to obtain a high clarification effect, the lower limit of the total content of the SnO ₂ component, the CeO ₂ component, or both is preferably 0.01%, more preferably 0.05%, and Most preferably, it is 1%.
On the other hand, one or more selected from SnO ₂ component or CeO ₂ component is used to maintain the mechanical strength, to lower the specific gravity, to obtain a high clarification effect and to enhance the reboil suppression effect at the time of direct pressing. The upper limit of the content of is preferably 0.8%, more preferably 0.6%, and most preferably 0.4%.

As ₂ O ₃ component, Sb ₂ O ₃ component and Cl ⁻ , NO ⁻ , SO ₂ ⁻ and F ⁻ components act as fining agents, but they can be harmful to the environment, and their use should be avoided. The glass of the present invention can obtain a clarification effect even if it does not contain an As ₂ O ₃ component or an Sb ₂ O ₃ component, and when these components and the clarifier component of the present application are added, the clarification effect is achieved between the clarifiers. Will be offset.
The PbO component is preferably not included because it is harmful to the environment and the specific gravity of the glass increases. Even if the glass of the present invention does not contain a PbO component, excessive precipitation of crystals is prevented, and the melting property is improved and the glass stability during molding is improved.
The Cs ₂ O component is preferably not included because the raw material cost is high, the ionic radius is large, and chemical strengthening is difficult.

Gd ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Nb ₂ O ₅ , Ga ₂ O ₃ , and WO ₃ components contribute to lowering the viscosity of glass, improving mechanical properties by improving Young's modulus, and improving heat resistance Therefore, although it can be added as an optional component, an increase in the amount added causes an increase in specific gravity and an increase in raw material cost. Accordingly, the total amount of one or more of these components is sufficient up to 5%. If the total amount exceeds 5%, the specific gravity, Young's modulus and specific rigidity cannot be satisfied. Therefore, the upper limit of the total amount of these components is preferably 5%, more preferably 4%, and most preferably 3%.

Components such as V, Cu, Mn, Cr, Co, Mo, Ni, Te, Pr, Nd, Er, Eu, and Sm, which are used as coloring components of glass, are obtained by utilizing the fluorescence characteristics resulting from these components. Can be added for the purpose of preventing mixing with other types of glass at a factory, etc., but this causes an increase in specific gravity, an increase in raw material costs, and a decrease in glass forming ability. The total amount of one or more of these components is sufficient up to 3%. Therefore, the upper limit of the total amount of these components is preferably 3% on the oxide basis, more preferably 2%, and most preferably 1%.

When the glass substrate of the present invention is a crystallized glass, it contains at least one selected from RAl ₂ O ₄ , R ₂ TiO ₄ (wherein R is one or more selected from Zn, Mg, Fe) as a crystal phase. The crystallinity of the precipitated crystals is preferably 1% to 15% and the crystal grain size is preferably 0.5 nm to 20 nm. Crystallized glass having these as the main crystal phase has a spinel structure, and the spinel itself has an excellent Mohs hardness of 8, so that excellent mechanical strength can be obtained. When the diameter is in the above range, it is possible to obtain a well-balanced surface smoothness and mechanical strength such as Young's modulus, Vickers hardness, and fracture toughness required for the next-generation information recording medium substrate. . In order to obtain the above effect, the crystallinity is more preferably 2% to 14%, and most preferably 3% to 13%. Similarly, the crystal grain size is more preferably 0.5 nm to 15 nm, and most preferably 0.5 nm to 10 nm. Similarly, in order to obtain the above effect, the maximum grain size of the main crystal phase is preferably 30 nm or less, more preferably 20 nm or less, and most preferably 15 nm or less.

Here, the “main crystal phase” refers to a crystal phase corresponding to a main peak (highest peak) in XRD diffraction. Analysis by X-ray diffraction makes it difficult to distinguish garnite (ZnAl ₂ O ₄ ) and spinel (MgAl ₂ O ₄ ) because the peaks appear at the same angle. The same applies to R ₂ TiO ₄ .

  “Crystallinity” can be obtained by adding up the amount (mass%) of crystals calculated from the diffraction intensity obtained from powder XRD using the Rietveld method. Regarding the Rietveld method, the “Crystal Analysis Handbook” Editorial Committee edited by the Crystallographic Society of Japan, “Crystal Analysis Handbook”, Kyoritsu Publishing Co., Ltd., September 1999, p. The method described in 492-499 was used.

“Crystal grain size” means that an image of an arbitrary part at a magnification of 100,000 to 500,000 is acquired with a TEM (transmission electron microscope), and the crystals appearing in the obtained image are sandwiched between two parallel straight lines. It is the average value of the longest distance. At this time, the n number is 100.
“Maximum crystal grain size” means that an image of an arbitrary part at a magnification of 100,000 to 500,000 times is acquired by a TEM (transmission electron microscope), and crystals appearing in the obtained image are expressed by two parallel straight lines. The maximum value of the longest distance when sandwiched. At this time, the n number is 100.

The Vickers hardness is a value representing the hardness of the substrate surface, and is specifically a value obtained by measurement by the following method. That is, by pressing a diamond square cone indenter with a face angle of 136 ° at a load of 4.90 N for 15 seconds and dividing the test load of 4.90 (N) by the surface area (mm ² ) calculated from the length of the indentation. Desired. For the measurement, a micro hardness tester MVK-E manufactured by Akashi Seisakusho Co., Ltd. can be used.

The value obtained by the SEPB method (JIS R1607) is used for the fracture toughness (K _1C ).
The fracture toughness value K _1C is preferably 1.0 or more, more preferably 1.1 or more, and preferably 1.2 or more in order to be applicable as a next-generation information recording medium substrate. Most preferred.

In order to avoid the influence of fluttering on high rotation in recent years as much as possible, in the case of a glass substrate having a Young's modulus of less than 85 GPa, for example, in the case of a 2.5-inch compatible substrate, the substrate thickness has conventionally been 0.635 mm. On the other hand, fluttering tends to be prevented by increasing the thickness of the substrate to 0.8 mm. Under such circumstances, a material capable of being used at a conventional substrate thickness of 0.635 mm is required for a substrate having a high Young's modulus, even if the substrate specific gravity is a somewhat high value. ing. In order to reduce the load applied to the spindle motor under such circumstances and to obtain a balance between specific gravity and mechanical strength that can be applied as a substrate for the next generation information recording medium, Successful rate optimization.

The glass substrate of the present invention can suppress damage due to alkali migration to the magnetic film formed on the substrate surface by substituting with other components having an ionic radius larger than the ions present on the substrate surface.
In addition, it is possible to suppress the breakage of the substrate based on the microcracks generated during the processing of the substrate end face.
In particular, alkali migration is often caused by elution of alkali components from the end face of the substrate on which a magnetic film or the like is not formed.
For this reason, it is particularly preferable to reduce the Li content in the vicinity of the end face of the substrate, and oxidation of the Li component in the region up to 5 μm inward from the end face of the glass substrate for information recording medium (hereinafter referred to as “end face region”). The content ratio α% based on the physical standard and a region that is 5 μm or more in the thickness direction from the two main surfaces of the glass substrate for information recording medium and that exceeds 5 μm in the center direction from the end surface of the substrate (hereinafter “ It is preferable that the ratio α / β of the content ratio β% of the Li component in the “internal region”) is α / β ≦ 1.
In the case of a composition not containing Li, the Na content may be confirmed by the above method.
In actual measurement, for example, a part of glass in the end face region and the inner region may be sampled, and the Li content may be mainly used by the ICP-AES method.

In actual production, the substrate after polishing is subjected to ion exchange treatment, and Li ⁺ or Na ⁺ is replaced with other components, for example, Na ⁺ or K ⁺ , so that the content ratio of Li or Na component is set to the above. be able to. In the case of crystallized glass, in addition to high mechanical properties in advance due to precipitated crystals, more desirable strength can be obtained by ion exchange treatment. In this case, sufficient strength can be obtained even if the compressive stress layer formed by ion exchange treatment (chemical strengthening) on the two main surfaces of the crystallized glass substrate is less than 30 μm.

More specifically, the glass substrate of the present invention is produced by the following method.
First, mix the raw materials such as oxides, carbonates and nitrates so as to have the glass components in the above composition range, and use a normal melting apparatus using a crucible such as platinum or quartz, the viscosity of the glass melt Dissolves at a temperature of 1.5 to 3.0 dPa · s.
Next, the temperature of the glass melt is raised to a temperature at which the viscosity becomes 1.0 to 2.3 dPa · s, preferably 1.2 to 2.2 dPa · s, and bubbles are generated in the glass melt and stirred. Causes effects and improves homogeneity.
Thereafter, the temperature of the glass melt is lowered to a temperature at which the viscosity becomes 1.8 to 2.6 dPa · s, preferably 2.0 to 2.5 dPa · s, and the defoaming of bubbles generated inside the glass is eliminated. Clarify, then maintain this temperature.

The molten glass produced under the above conditions is dropped onto the lower mold, and the molten glass is pressed (direct press) with the upper and lower molds to form a disk having a thickness of about 0.7 mm to 1.2 mm. Specifically, the upper mold temperature is set to 300 ± 100 ° C., preferably 300 ± 50 ° C., and the lower mold temperature is set to Tg ± 50 ° C., preferably Tg ± 30 ° C. of the glass.
Furthermore, the temperature of the glass outlet pipe for guiding the glass from the crucible to the press-molded shape is set to a temperature at which the viscosity of the glass is 2.0 to 2.6 dPa · s, preferably 2.1 to 2.5 dPa · s. Then, a predetermined amount of glass is dropped on the lower mold, and the upper mold and the lower mold are brought close to each other and pressed to obtain a glass molded body.
In manufacturing an information recording medium substrate, since cost reduction per sheet is required, the press speed is 150 to 700 mm / sec, and the cycle time (time from the start of pressing to the start of the next press) is 1 to 2.3 sec. The glass of the present invention is used even in such a shock during pressing, and the temperature of the glass melt and the manufacturing equipment is controlled as described above, thereby suppressing the occurrence of reboil during pressing. It becomes possible to do.

  In addition, it can also be produced by a method of slicing a glass body formed into a cylindrical shape, a method of cutting out a glass sheet produced by a float method, or the like. However, the production by direct press is most preferable in terms of production efficiency.

When crystallized glass is used, the resulting disk-shaped glass is crystallized by heat treatment. This heat treatment is preferably performed at two stages. That is, first, a nucleation step is performed by heat treatment at a first temperature, and after this nucleation step, a crystal growth step is performed by heat treatment at a second temperature higher than the nucleation step.
In this crystallization step, it is preferable that disk-shaped ceramic setters and disk-shaped glass are alternately stacked and sandwiched between the setters (the number of setters is the number of glasses + 1) because the flatness of the disk is improved.
In order to obtain the grain size and crystallinity of the precipitated crystal of the present invention, preferable heat treatment conditions are as follows.
The maximum temperature of the first heat treatment is preferably 600 ° C to 750 ° C. The first stage heat treatment may be omitted. The maximum temperature of the second stage heat treatment is preferably 650 ° C to 850 ° C.
The holding time of the first temperature is preferably 1 hour to 10 hours.
The holding time of the second temperature is preferably 1 hour to 10 hours.

  Next, preferred embodiments of the present invention will be described.

  The glass of the above embodiment of the present invention is prepared by mixing raw materials of oxide and carbonate, and melting the raw material using a quartz or platinum crucible at a temperature of about 1250 to 1450 ° C. After sufficiently dissolving so as not to cause unmelted residue, the temperature is raised to a temperature of about 1350 to 1500 ° C. and then lowered to a temperature of 1,450 to 1,250 ° C., and the bubbles generated inside the glass are defoamed and clarified. Made. After that, a predetermined amount of glass flows out while maintaining the temperature, and the upper mold temperature is set to 300 ± 100 ° C. and the lower mold temperature is set to Tg ± 50 ° C. by direct press method. A glass molded body was obtained. Subsequently, the obtained glass molded body was lapped, polished and washed with hydrofluoric acid for removing the abrasive by the above-mentioned method to obtain a substrate for an information recording medium. At this time, the surface roughness Ra (arithmetic mean roughness) of the substrate was all 1 or less. The surface roughness Ra (arithmetic average roughness) was measured with an atomic force microscope (AFM).

In Tables 1 to 3, the glass compositions (mol%) of Examples 1 to 6 and Comparative Examples 1 to 7, specific gravity of the substrate after press molding, Vickers hardness, Young's modulus, ratio of Young's modulus to specific gravity (E / ρ), The average linear expansion coefficient ((alpha)) in 25 to 100 degreeC is shown.
The average linear expansion coefficient was measured by changing the temperature range from 25 ° C. to 100 ° C. according to JOGIS (Japan Optical Glass Industry Association Standard) 16-2003 “Measurement Method of Average Linear Expansion Coefficient of Optical Glass Near Room Temperature”. Value.
Specific gravity was measured using Archimedes method, and Young's modulus was measured using ultrasonic method.
The Vickers hardness was obtained by dividing a load (N) when a pyramid-shaped depression was made on a test surface by using a diamond square cone indenter having a facing angle of 136 ° by a surface area (mm ² ) calculated from the length of the depression. Indicated by value. Using a micro hardness tester MVK-E manufactured by Akashi Seisakusho Co., Ltd., the test load was 4.90 (N) and the holding time was 15 (seconds).

(Example 7)
With respect to the crystallized glass composition of Example 1, a 2.5-inch HDD polishing substrate (65φ × 0.800 mmt) was prepared by a known method through a polishing step including a chemical strengthening treatment step, and the substrate surface was 3 μm ² by AFM. When observed in the field of view, it was Ra 0.78 mm, Rmax 8.9 mm, and micro waveness (μWa) 0.45 mm, and it was confirmed that the surface properties required for the next-generation HDD substrate were extremely excellent.

Microwaveness (μWa) is one of the factors that affect the electromagnetic conversion characteristics of magnetic recording media. In order to improve the electromagnetic conversion characteristics, the microwaveness needs to be reduced as well as Ra. is there.
For example, the measurement of the micro waveness is performed under the condition of a band pass filter of 50 to 200 nm by the optical interferometry (device name: Micro XAM) in the circumferential direction in the 0 °, 90 °, 180 °, and 270 ° directions of the upper and lower surfaces of the substrate The method implemented by is mentioned. Actual measurement is not limited to this.

(Example 8)
Further, a chromium alloy underlayer and a cobalt alloy magnetic layer are formed on the substrate obtained by the above-described example by DC sputtering, and further a diamond-like carbon layer is formed, and then a perfluoropolyether lubricant is added. This was coated to obtain an information magnetic recording medium.

  A substrate such as a magnetic recording medium substrate of the present invention is a substrate corresponding to an increase in surface recording density, with less surface contamination, excellent recording / reproducing characteristics after film formation, extremely low error rate. It was confirmed that there was.

  For Examples 1, 3, and 4 and Comparative Examples 1, 2, and 4, the surface of the polished substrate was subjected to OSA (Optical Surface Analysis) inspection. Specifically, the substrate surface is irradiated with light having a wavelength of 405 nm and a wavelength of 632 nm, and foreign matter is detected from the scattered light. The results are shown in Table 3. The weather resistance test is a result of observation of the substrate surface after a test at a temperature of 90 ° C. and a humidity of 5% after a holding time of 480 hours. In Examples 1, 3, and 4, the number of foreign substances on the substrate surface is small, and there is almost no change after the weather resistance test. On the other hand, in Comparative Examples 1, 2, and 4, the number of foreign matters on the substrate surface is large, and the number of foreign matters on the substrate surface increases extremely after the weather resistance test. This is because alkali components, particularly lithium components, are deposited on the substrate surface.

Claims (4)

When expressed in mol% on an oxide basis, as a glass component, a SiO ₂ 40 mol% or more 80 mol% or less, _Al 2 _{O 3} of 3 mol% or more 12 mol% or less, Na ₂ O less 2.20 mol% or more 10 mol% Contains,
The R ₂ O component content is 10 mol% or less (R; one or more selected from Li, Na, K), and the R′O component content is 15 mol% or more (R ′; Mg, Ca, Zn, One or more selected from Ba, Sr, and Fe),
A crystallized glass containing one or more selected from RAl ₂ O ₄ and R ₂ TiO ₄ (wherein R is one or more selected from Zn, Mg and Fe) as a crystal phase,
A glass characterized in that the surface zeta potential measured using an aqueous solution in which Na ₂ SO ₄ is mixed as a buffer and the pH is adjusted to 10 with H ₂ SO ₄ and NaOH is lower than −50 mV. substrate. However, the electric potential of the electrically neutral region of the aqueous solution sufficiently separated from the surface of the glass substrate is set to 0V. _{2. The} surface zeta potential measured using an aqueous solution in which Na ₂ SO ₄ is mixed as a buffer and the pH is adjusted to 2 with H ₂ SO ₄ and NaOH is negative. Glass substrate. However, the electric potential of the electrically neutral region of the aqueous solution sufficiently separated from the surface of the glass substrate is set to 0V. In the potential difference between the substrate surface and the cerium oxide particles measured using an aqueous solution containing cerium oxide particles, mixed with Na ₂ SO ₄ as a buffer, and adjusted in pH with H ₂ SO ₄ and NaOH, the aqueous solution 3. The glass substrate according to claim 1, wherein the maximum value of the potential difference when measured by changing the pH in a range of 10 to 12 is 20 mV or less. The potential difference between the surface of the substrate and the silica particles measured using an aqueous solution containing silica particles, mixed with Na ₂ SO ₄ as a buffer, and adjusted to pH ₄ with H ₂ SO ₄ and NaOH is 15 mV or more. The glass substrate according to claim 1, wherein the glass substrate is provided.